how an electric iron doesn’t have an efficiency of 100%


Thermodynamics won’t allow anything to have an efficiency of 100% because some energy will be converted to heat. What about electric irons and pretty much any other heating equipment that has a working principle revolving around losing energy to heat

In: 0

This is a problem with definitions of what your machine does. If you define a machine as a heater, or electric iron in your example, and the only constraint is that energy eventually becomes heat than yes it is 100% efficient. But is that really a useful definition? If you think about it any machine is a heater in that sense.

So in reality it makes more sense to talk about work done rather than just where the energy ends up. In this case some energy will be lost to sound or light and not do any work, leading to <100% efficiency.

Yep, heaters etc have an efficiency of 100%. Only time they don’t is if they are running a fan but the drop wouldn’t be by much at all. I guess technically if a heater is making a constant creaking noise that wouldn’t be 100% but it would still be 99.99*% with a whole lot of 9s.

I guess an argument would be made that an iron or any other focused heat system isn’t 100% because some heat would go to the handle and body etc and not the part you want hot.

Also as you would expect. Heat pump based heaters are more than 100% efficient. Usually 200-500% because you get more heat energy than you put into it.

So it really depends on how you measure.

Efficiency is “the ratio between *usable* work done compared to the input energy”

So while this is a real thing that we can objectively measure. What you consider “usable” is something that you get to decide. (I would like to point out we have plenty of standards in place though to make sure it’s somewhat consistent)

So going back to talking about an electric iron. You are correct that 100% of the energy that goes into that will end up as heat. But I suspect that the only “usable” part is the heat that goes into unwrinkling your clothes.

So there’s all the heat that ends up *not* doing that that could be considered waste heat. And therefore you can have an efficiency of less than 100% I have no idea what the exact numbers are though. Can’t find too much literature about it.

Everything glows very slightly. The hotter something is the higher energy and frequency the light has. When things are cooler than red hot they still radiate some light, but it is too low energy too see.

An iron also sends heat in all directions and not just down.

The wires sending the electricity to the iron as well as the powerplant have some loss.

If you listen closely, almost every heating element emits noise. At higher temps they also emit light.